JP5019000B2 - Multilayer structure - Google Patents

Description

  The present invention relates to a multilayer structure in which a layer made of a blend of an ethylene-vinyl alcohol copolymer and a maleic anhydride-modified olefin resin is provided as an intermediate layer. Concerning the structure.

  Polyolefin resins such as polyethylene and polypropylene, and polyester resins represented by polyethylene terephthalate have excellent properties such as moldability, transparency, mechanical strength, and chemical resistance, and packaging materials such as films, sheets, and bottles. Is used in various fields.

  By the way, an ethylene-vinyl alcohol copolymer (ethylene-vinyl acetate copolymer saponified product) is known as a resin excellent in oxygen barrier properties, and particularly in the field of packaging materials, the above-mentioned polyolefin resins and polyesters are used. A multilayer structure in which a resin is used as an inner and outer layer and an ethylene-vinyl alcohol copolymer layer as an intermediate layer (oxygen barrier resin layer) is widely used in practical use.

  Recently, the inner and outer layers described above have an oxygen-absorbing resin layer containing an oxidizing organic component of an ethylenically unsaturated group-containing polymer (for example, polybutadiene) and a transition metal catalyst component such as iron or cobalt as an intermediate layer. A multilayer structure provided between the two is also put to practical use as an excellent oxygen barrier property (see, for example, Patent Document 1).

  By the way, although ethylene-vinyl alcohol copolymer is excellent in oxygen barrier property, it has a drawback of poor adhesion to other resins, so that it is adjacent to such an ethylene-vinyl alcohol copolymer layer. It is necessary to provide an adhesive layer. For example, in the multilayer structure having an oxygen-absorbing resin layer proposed in Patent Document 1, oxygen absorption is performed to compensate for a decrease in oxygen-absorbing ability (decrease in oxygen barrier properties) over time of the oxygen-absorbing resin layer. The ethylene-vinyl alcohol copolymer is used as the resin substrate of the conductive resin layer, and the ethylene-vinyl alcohol copolymer layer is provided on both sides of the oxygen-absorbing resin layer. Has a structure bonded to the inner and outer layers via an adhesive layer. As described above, in order to use the ethylene-vinyl alcohol copolymer, an unnecessary adhesive layer is originally required in order to improve the function as a packaging material, and the layer structure becomes complicated, and adhesion An extruder for forming the agent layer is required, resulting in an increase in production cost and the like, and an improvement is demanded.

  As a packaging material in which the above problems have been solved, Patent Document 2 proposes a multilayer structure provided with an intermediate layer made of a blend of an ethylene-vinyl alcohol copolymer and a polyester resin.

JP 2007-320576 A Japanese Patent No. 3788442

  In the multilayer structure proposed in Patent Document 2, the intermediate layer itself of the blend of the ethylene-vinyl alcohol copolymer and the polyester resin has an adhesive property as well as an oxygen barrier property. Although it has the advantage that it is not necessary to provide an agent layer, the intermediate layer exhibits excellent adhesion to the inner and outer layers only when a polyester resin such as polyethylene terephthalate is used as the inner and outer layers. However, when a polyolefin-based resin is used as the inner and outer layers, the intermediate layer of such a blend exhibits little adhesion to the inner and outer layers and is prone to delamination. It becomes necessary to provide an adhesive layer.

  Further, by applying the means proposed in Patent Document 2, it is conceivable that an ethylene-vinyl alcohol copolymer blended with a polyolefin resin is provided as an intermediate layer. Polyolefin resin is particularly poor in compatibility, and it is difficult to uniformly distribute the ethylene-vinyl alcohol copolymer in the blend, and the excellent oxygen barrier property of the ethylene-vinyl alcohol copolymer is sufficient. In order to exhibit an excellent oxygen barrier property, it is necessary to use a large amount of an ethylene-vinyl alcohol copolymer. Therefore, in this case, the inner and outer layers (polyolefin type) In the end, this means that the inner and outer layers are made of polyolefin resin. Can not be applied to the case was.

  Therefore, the object of the present invention is to sufficiently exhibit the excellent oxygen barrier property of the ethylene-vinyl alcohol copolymer without providing a special adhesive layer, and use polyolefin resin as the inner and outer layers. It is an object of the present invention to provide a multilayer structure that can be effectively applied even in the case of the above.

  As a result of conducting many experiments on the above problems, the present inventors use a blend of an ethylene-vinyl alcohol copolymer and a maleic anhydride-modified olefin resin widely used as an adhesive as an intermediate layer. When both components are distributed in a state of forming a clear interface, not only excellent oxygen barrier properties but also excellent adhesion to inner and outer layers formed of polyolefin resins are expressed. As a result, the present inventors have completed the present invention.

  That is, according to the present invention, a multilayer in which an adhesive intermediate layer made of a blend of an ethylene-vinyl alcohol copolymer (A) and a maleic anhydride-modified olefin resin (B) is provided between the inner and outer layers. A structure, wherein the adhesive intermediate layer comprises an ethylene-vinyl alcohol copolymer (A) and a maleic anhydride-modified olefin resin (B) in a weight ratio of 4: 6 to 8: 2. In a scanning electron microscopic photograph of the cross section in the thickness direction of the multilayer structure, image-analysis software is used to use the ethylene-vinyl alcohol copolymer (A) and maleic anhydride-modified olefin resin (B) in the adhesive intermediate layer. When the contrast distribution in the vicinity of the interface is quantified, a multilayer structure characterized by exhibiting a standard deviation of 65 or more is provided.

In the multilayer structure of the present invention,
(1) The phase structure of the adhesive intermediate layer is a sea-island structure using the maleic anhydride-modified olefin resin (B) as the sea, or an ethylene-vinyl alcohol copolymer (A) and a maleic anhydride-modified olefin resin (B). Both are both continuous phases that exist as continuous phases,
(2) At least one of the inner and outer layers is formed of a polyolefin resin,
(3) A gas barrier intermediate layer comprising an oxygen-absorbing resin layer or an oxygen barrier resin layer is provided between the inner and outer layers, and adjacent to the inner layer side and the outer layer side of the gas barrier intermediate layer. The adhesive intermediate layer is provided,
(4) The gas barrier intermediate layer contains an ethylene-vinyl alcohol copolymer as a resin base material,
(5) In the adhesive intermediate layer, the ethylene-vinyl alcohol copolymer (A) and the maleic anhydride-modified olefin resin (B) have the following formula:
η _AB = a / b
Where a is an ethylene-vinyl alcohol at 200 ° C. and a shear rate of 200 s ^−1.
The melt viscosity of the copolymer (A),
b is maleic anhydride modified at 200 ° C. and a shear rate of 200 s ⁻¹
The melt viscosity of the olefin resin (B).
The viscosity ratio η _AB defined by is in the range of 3-10,
(6) An odor scavenger is blended in the inner layer,
Is preferred.

According to the present invention, a multilayer in which an adhesive intermediate layer made of a blend of an ethylene-vinyl alcohol copolymer (A) and a maleic anhydride-modified olefin resin (B) is provided between the inner and outer layers. A structure,
The ethylene-vinyl alcohol copolymer (A) and the maleic anhydride-modified olefin resin (B) are represented by the following formula:
η _AB = a / b
Where a is an ethylene-vinyl alcohol at 200 ° C. and a shear rate of 200 s ^−1.
The melt viscosity of the copolymer (A),
b is maleic anhydride modified at 200 ° C. and a shear rate of 200 s ⁻¹
The melt viscosity of the olefin resin (B).
A multilayer structure is provided in which the viscosity ratio η _AB defined by is in the range of 3 to 10.

  In the multilayer structure of the present invention, it is remarkable that a layer made of a blend of the ethylene-vinyl alcohol copolymer (A) and the maleic anhydride-modified olefin resin (B) is provided between the inner and outer layers. Such a blend layer not only exhibits excellent oxygen barrier properties due to the ethylene-vinyl alcohol copolymer, but also against the inner and outer layers, particularly against the inner and outer layers formed from polyolefin resins. However, it is an adhesive intermediate layer exhibiting excellent adhesiveness. That is, the multilayer structure of the present invention can exhibit the excellent oxygen barrier property of the ethylene-vinyl alcohol copolymer without providing a special adhesive layer in order to prevent delamination, etc. It is particularly suitably applied as a packaging material for containers and caps.

In the present invention, the adhesive intermediate layer formed between the inner and outer layers is selected and combined so that the viscosity ratio η _AB defined by the above formula is in the range of 3 to 10. When the copolymer (A) and the maleic anhydride modified olefin resin (B) are formed, the oxygen barrier property of the ethylene-vinyl alcohol copolymer (A) and the maleic anhydride modified olefin resin (B) Therefore, the adhesion to the inner and outer layers can be improved simultaneously with the oxygen barrier property without providing a special adhesive layer.

It is a figure which shows typically the thickness direction cross-section observation photograph of the intermediate | middle layer which consists of a blend of ethylene-vinyl alcohol copolymer (A) and maleic anhydride modified olefin resin (B), (a) is this invention. It is an example and (b) is a comparative example outside the scope of the present invention. It is an electron micrograph which shows the phase structure of the ethylene-vinyl alcohol copolymer and maleic anhydride modified olefin resin in an adhesive intermediate | middle layer, (a) is an example of this invention, (b) is outside the range of this invention. It is a comparative example.

<Principle of the present invention>
In the multilayer structure of the present invention, the intermediate layer made of a blend of the ethylene-vinyl alcohol copolymer (A) and the maleic anhydride-modified olefin resin (B) not only exhibits excellent oxygen barrier properties, but also the inner and outer layers. In order to exhibit such an oxygen barrier property and adhesiveness, ethylene-vinyl alcohol copolymer (A) and anhydrous maleic acid are exhibited. In the scanning electron microscopic photograph of the cross section in the thickness direction of the multilayer structure at the same time as containing the acid-modified olefin resin (B) at a predetermined quantitative ratio (4: 6 to 8: 2), When the contrast distribution in the vicinity of the interface between the ethylene-vinyl alcohol copolymer (A) and the maleic anhydride-modified olefin resin (B) in the layer is measured, the standard deviation is 65 or more, particularly 70 or more. It is necessary to show.

That is, in the phase structure photograph composed of the above blend, in FIGS. 1 (a) and 1 (b) schematically showing an observation photograph in the vicinity of the interface between both components, the central bright portion is an ethylene-vinyl alcohol copolymer (A). Is a portion where the maleic anhydride-modified olefin resin (B) is present. In such a cross-sectional observation photograph, the contrast distribution in the thickness direction shows a large standard deviation as described above. As shown in FIG. 1A, the brightness of both components is clear. This means that the interface between the two components is clearly present. On the other hand, when the standard deviation of the contrast distribution is smaller than the above range, the difference in brightness between the two components is small, and the interface between the two components is unclear as shown in FIG. To do.
The contrast distribution in the cross-sectional observation photograph as described above can be measured by image analysis software.

  As understood from the above description, the adhesive intermediate layer in the multilayer structure of the present invention is clearly defined between the two components (A) and (B) as shown in FIG. Since the interface exists, as shown in Example 1 described later, together with excellent oxygen barrier properties, it exhibits excellent adhesion to the inner and outer layers of the polyolefin-based resin, without providing an adhesive layer, Inconveniences such as delamination can be effectively avoided. On the other hand, even if the intermediate layer is formed from a blend of the ethylene-vinyl alcohol copolymer (A) and the maleic anhydride-modified olefin resin (B), two components as shown in FIG. When the interface between (A) and (B) is unclear, the oxygen barrier properties are unsatisfactory as in Comparative Example 1 described later, and the adhesion to the inner and outer layers of the polyolefin resin is also low. It will be significantly lower.

  Thus, the standard deviation of the contrast distribution between the ethylene-vinyl alcohol copolymer (A) and the maleic anhydride-modified olefin resin (B) is in the above range, and a clear interface is formed between the two components. The reason for the excellent gas barrier properties and excellent adhesion to the inner and outer layers is not clearly understood, but there is probably a clear interface between the two components. This means that both components are incompatible and exist in independent forms. As a result, the ethylene-vinyl alcohol copolymer (A) has excellent oxygen barrier properties and the maleic anhydride-modified olefin resin (B). It is presumed that all of the properties as an adhesive are sufficiently exhibited. That is, when the standard deviation of the contrast distribution is small and the interface between the two components is unclear, both components are compatible. As a result, the oxygen barrier of the ethylene-vinyl alcohol copolymer (A) Therefore, it is considered that the properties of the maleic anhydride-modified olefin resin (B) as an adhesive also deteriorate.

Further, as described above, the ethylene-vinyl alcohol copolymer (A) and maleic anhydride, which are selected and combined so that the viscosity ratio η _AB defined by the above formula is in the range of 3 to 10 When an adhesive intermediate layer is formed with the modified olefin resin (B), the adhesive intermediate layer has a sea-island structure or an ethylene-vinyl alcohol copolymer with the maleic anhydride-modified olefin resin (B) as the sea. A bicontinuous structure in which both (A) and the maleic anhydride-modified olefin resin (B) are present as a continuous phase is formed. As a result, the functions of both components (A) and (B) are not impaired, and the oxygen barrier property of the ethylene-vinyl alcohol copolymer (A) and the adhesiveness of the maleic anhydride-modified olefin resin (B) are independent. Thus, the adhesiveness to the inner and outer layers can be improved simultaneously with the oxygen barrier property without providing a special adhesive layer.

<Adhesive intermediate layer>
In the present invention, the ethylene-vinyl alcohol copolymer (A) used for the formation of the adhesive intermediate layer is itself, that is, in the field of packaging materials, except for the conditions relating to fluidity described later. The grade used as an oxygen barrier resin is used.

  Specifically, an ethylene-vinyl acetate copolymer having an ethylene content of 20 to 60 mol%, particularly 25 to 50 mol%, is saponified so that the saponification degree is 96% or more, particularly 99 mol% or more. The saponified copolymer obtained is preferably used. The ethylene-vinyl alcohol copolymer (saponified ethylene-vinyl acetate copolymer) should have a molecular weight sufficient to form a film, and is generally a mixed solvent having a phenol / water weight ratio of 85/15. In particular, it is desirable to have an intrinsic viscosity of 0.01 dl / g or more, particularly 0.05 dl / g or more, measured at 30 ° C.

  The maleic anhydride-modified olefin resin, which is the other component forming the adhesive intermediate layer, has been conventionally used as an adhesive resin for forming an adhesive layer, for example, grafts modified with maleic anhydride. A modified olefin resin is used. In this case, polyethylene, polypropylene, and ethylene-α olefin copolymer are suitable as the olefin resin to be graft-modified. Further, in such maleic anhydride-modified olefin resin, from the viewpoint of adhesiveness, the amount of carbonyl group (> C═O) in the main chain or side chain is 1 to 200 meq / 100 g resin, particularly 1 to 50 meq / 100 g resin. It is preferable to contain.

  In the adhesive intermediate layer in the multilayer structure of the present invention, a blend of the ethylene-vinyl alcohol copolymer (A) and the maleic anhydride-modified olefin resin (B) is used in order to exhibit excellent oxygen barrier properties. The ratio (A: B) should be a weight ratio of 4: 6 to 8: 2, preferably 5: 5 to 6: 4, most preferably 7: 3 to 8: 2. That is, if the ethylene-vinyl alcohol copolymer (A) is used in a larger amount than the above range, the amount of the maleic anhydride-modified olefin resin (B) decreases, so even if the oxygen barrier property is good. In addition, the adhesiveness to the inner and outer layers, particularly to the polyolefin-based resin is lowered, and an adhesive layer must be provided to prevent delamination. On the other hand, when the amount of the maleic anhydride-modified olefin resin is larger than the above range, the adhesiveness to the inner and outer layers is sufficient, but the ethylene-vinyl alcohol copolymer (A) is small, so that the oxygen barrier As a result, the intermediate layer only functions as an adhesive layer.

  Further, in the present invention, the adhesive intermediate layer has a blend ratio of both components within the above-described predetermined range and is anhydrous in order to maintain the above-described excellent oxygen barrier property and have adhesiveness to the inner and outer layers. A sea-island structure with the maleic acid-modified olefin resin (B) as the sea or a phase structure in which both components (A) and (B) are continuously distributed in layers (bicontinuous phase structure) In particular, a bicontinuous phase is preferred in terms of oxygen barrier properties.

Furthermore, in the present invention, the adhesive intermediate layer having the sea-island structure or the continuous phase structure as described above has the following formula:
η _AB = a / b
Where a is an ethylene-vinyl alcohol at 200 ° C. and a shear rate of 200 s ^−1.
The melt viscosity of the copolymer (A),
b is maleic anhydride modified at 200 ° C. and a shear rate of 200 s ⁻¹
The melt viscosity of the olefin resin (B).
It can be formed by combining both components so that the viscosity ratio η _AB defined by is in the range of 3 to 10, particularly 3 to 7. That is, by combining both components so as to obtain such flow characteristics, when this blend is extruded or injected to form an adhesive intermediate layer, the oxygen barrier properties and adhesiveness of each component are impaired. Therefore, a sea-island structure in which the maleic anhydride-modified olefin resin (B) is used as the sea or a distribution structure in which any of the components are continuously formed in layers is easily formed.

By the way, in the present invention, in this adhesive intermediate layer, the standard deviation of the contrast distribution between the ethylene-vinyl alcohol copolymer (A) and the maleic anhydride-modified olefin resin (B) is within a predetermined range. By forming a clear interface between them, the adhesion to the inner and outer layers and the oxygen barrier property can be further improved. For this purpose, the ethylene-vinyl alcohol copolymer (A) and the maleic anhydride-modified olefin resin (B) are selected at the same time as satisfying the quantity ratio and viscosity ratio η _AB as described above, and at the same time, the molding temperature. In particular, the melt kneading temperature, shear heat generation, and die temperature in a cylinder of an extruder or the like should be relatively low. Under the molding conditions in which excessive temperature is applied, the reactivity between the ethylene-vinyl alcohol copolymer (A) and the maleic anhydride-modified olefin resin (B) is increased in the extruder, and the compatibilization proceeds. It is presumed that the interface between the two components becomes unclear due to the low standard deviation of the above, and as a result, the adhesion to the inner and outer layers and the oxygen barrier property are not further improved.

  In addition, since the acid modification rate of the maleic anhydride-modified olefin resin (B) also greatly affects the adhesiveness, the maleic anhydride-modified olefin resin (B) to be used is generally 1 to 200 meq / 100 g in the main chain or side chain. It preferably contains a carbonyl group (> C═O) in an amount of resin, especially 1 to 50 meq / 100 g resin (ie corresponding to acid modification rate). When the modification rate is higher than the above range, the reactivity becomes high, and problems such as the above-described decrease in adhesiveness and gel and sag occur, and when it is low, the function as an adhesive tends to be reduced.

  In the adhesive intermediate layer, additives such as a dispersant may be blended as needed to maintain transparency and moldability as long as the adhesiveness and oxygen barrier property are not impaired.

<Inner and outer layers>
In the multilayer structure of the present invention, the resin for forming the inner and outer layers is not particularly limited, and the inner and outer layers may be formed of various thermoplastic resins, particularly from the viewpoint of use as a packaging material. In particular, thermoplastic polyesters such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, which are particularly preferably used, can be used, but it is particularly preferable to use a polyolefin resin. That is, in the present invention, when the inner and outer layers are formed of a polyolefin-based resin, the excellent oxygen barrier property of the ethylene-vinyl alcohol copolymer that exhibits little adhesion to the polyolefin-based resin This is because the present invention can be effectively exhibited without causing inconveniences such as delamination, and the excellent effects of the present invention are maximized.

  Examples of such polyolefin resins include low density polyethylene (LDPE), medium density polyethylene (MDPE), high density polyethylene (HDPE), linear low density polyethylene (LLDPE), and linear ultra low density polyethylene (LVLDPE). Polyethylene, polypropylene, ethylene-propylene copolymer, polybutene-1, ethylene-butene-1 copolymer, propylene-butene-1 copolymer, ethylene-propylene-butene-1 copolymer, ethylene-vinyl acetate copolymer Examples thereof include a polymer and an ion-crosslinked olefin copolymer (ionomer).

  In addition, the various inner and outer layer forming resins as described above may be those of extrusion grade or injection grade that are conventionally used in the field of packaging materials. In particular, in order to suppress the generation of flow marks during multilayer molding, it is preferable to select a resin having a viscosity comparable to that of the adjacent layer.

  The inner layer and the outer layer do not need to be formed of the same kind of resin. For example, the outer layer may be formed of the above-described polyester resin and the inner layer may be formed of a polyolefin resin. Furthermore, in the inner and outer layers, a lubricant, a modifier, a pigment, an ultraviolet absorber and the like may be blended as necessary.

<Layer structure of multilayer structure>
The multilayer structure of the present invention may have an arbitrary layer structure as long as the adhesive intermediate layer described above is provided between the inner and outer layers, and an appropriate layer structure according to the application. You may have. In such a layer structure, as the simplest layer structure,
Although a three-layer structure of inner layer / adhesive intermediate layer / outer layer can be mentioned, in order to further enhance the oxygen barrier property, a structure provided with a gas barrier intermediate layer is preferable.
A five-layer structure of inner layer / adhesive intermediate layer / gas barrier intermediate layer / adhesive intermediate layer / outer layer may be employed.

  In the five-layer structure as described above, examples of the gas barrier layer include an oxygen barrier resin layer or an oxygen absorbent resin layer.

  The oxygen-barrier resin that forms the oxygen-barrier resin layer is typically the above-described ethylene-vinyl alcohol copolymer, and in particular, the oxygen-barrier resin layer formed from the ethylene-vinyl alcohol copolymer is described above. Adhesiveness with the adhesive intermediate layer is the highest and is extremely suitable. The ethylene-vinyl alcohol copolymer may be the same as the ethylene-vinyl alcohol copolymer used for forming the adhesive intermediate layer.

  Examples of oxygen barrier resins other than ethylene-vinyl alcohol copolymers include nylon 6, nylon 6/6, nylon 6/6/6 copolymer, metaxylylene adipamide (MXD6), nylon 6 -Polyamides, such as 10, nylon 11, nylon 12, nylon 13, etc. can be mentioned. Among these polyamides, those having the number of amide groups per 100 carbon atoms in the range of 5 to 50, particularly 6 to 20 are preferable in that they have high oxygen barrier properties. These polyamides should also have a molecular weight sufficient to form a film. For example, in concentrated sulfuric acid (concentration 1.0 g / dl), the relative viscosity measured at 30 ° C. is 1.1 or more, particularly 1.5 or more. It is desirable to be.

  The oxygen-absorbing resin layer is a resin layer containing an oxidizing organic component and a transition metal catalyst component, and is usually a material in which an oxidizing organic component and a transition metal catalyst are dispersed in a base resin, It may be a known one disclosed in Patent Document 1 and the like. That is, the oxidizing organic component has a function of blocking oxygen when it is oxidized by absorbing oxygen, and the transition metal catalyst component is blended to promote oxidation of the oxidizing organic component.

  For example, examples of the oxidizing organic component include an ethylenically unsaturated group-containing polymer. This polymer has a carbon-carbon double bond, and this double bond portion is easily oxidized by oxygen, whereby oxygen is absorbed and trapped.

Such an ethylenically unsaturated group-containing polymer is derived from, for example, polyene as a monomer, and a suitable example of polyene used as a single monomer is not limited thereto. Although not, the following can be illustrated.
Conjugated dienes such as butadiene and isoprene;
1,4-hexadiene, 3-methyl-1,4-hexadiene, 4-methyl 1,4-hexadiene, 5-methyl-1,4-hexadiene, 4,5-dimethyl-1,4-hexadiene, 7- Chain non-conjugated dienes such as methyl-1,6-octadiene;
Methyltetrahydroindene, 5-ethylidene-2-norbornene, 5-
Cyclic non-conjugated dienes such as methylene-2-norbornene, 5-isopropylidene-2-norbornene, 5-vinylidene-2-norbornene, 6-chloromethyl-5-isopropenyl-2-norbornene, dicyclopentadiene;
2,3-diisopropylidene-5-norbornene, 2-ethylidene-3-
Trienes such as isopropylidene-5-norbornene and 2-propenyl-2,2-norbornadiene, chloroprene;

That is, a homopolymer of the above polyene, or a random copolymer, a block copolymer, or the like obtained by combining two or more of the above polyenes with other monomers can be used as the oxidizing polymer.
Examples of other monomers to be copolymerized with the polyene include α-olefins having 2 to 20 carbon atoms, specifically, ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-undecene, 1-dodecene, 1-tridecene, 1-tetradecene, 1-pentadecene, 1-hexadecene, 1-heptadecene, 1- Nonadecene, 1-eicosene, 9-methyl-1-decene, 11-methyl-1-dodecene, 12-ethyl-1-tetradecene and the like can be exemplified. Besides these, styrene, vinyltriene, acrylonitrile , Methacrylonitrile, vinyl acetate, methyl methacrylate, ethyl acrylate and the like can also be used.

  Examples of the oxidizing organic component include polybutadiene (BR), polyisoprene (IR), natural rubber, nitrile-butadiene rubber (NBR), styrene-butadiene rubber (SBR), and chloroprene among the polymers derived from the polyenes described above. Rubber, ethylene-propylene-diene rubber (EPDM), and the like are suitable, but of course not limited thereto. Moreover, the iodine value is good to be 100 or more, especially about 120-196.

  In addition to the above-mentioned ethylenically unsaturated group-containing polymer, a polymer that is easily oxidized, such as polypropylene and an ethylene / carbon oxide copolymer, can be used as the oxidizing organic component.

  From the viewpoint of moldability, it is preferable that the above-described oxidizing polymer or copolymer thereof has a viscosity at 40 ° C. in the range of 1 to 200 Pa · s.

  As described above, the transition metal catalyst is used to promote the oxidation of the oxidizing organic component, and is used in the form of a low-valent inorganic salt, organic salt or complex salt of the transition metal. The

  In such a fiber metal catalyst, the transition metal is preferably a group VIII metal such as iron, cobalt, nickel, etc., but also a group I metal such as copper, silver, tin, titanium, zirconium, etc. It may be a Group IV metal, a Group V metal such as vanadium, a Group VI metal such as chromium, a Group VII metal such as manganese, or the like. Among these, cobalt is particularly preferable because it significantly promotes oxygen absorption (oxidation of the oxidizing organic component).

  Examples of the inorganic salts of transition metals include halides such as chlorides, sulfur oxysalts such as sulfates, nitrogen oxysalts such as nitrates, phosphorus oxysalts such as phosphates, and silicates. .

  Examples of organic salts of transition metals include carboxylates, sulfonates, and phosphonates, and carboxylates are preferred for the purposes of the present invention. Specific examples thereof include acetic acid, propionic acid, isopropionic acid, butanoic acid, isobutanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, isoheptanoic acid, octanoic acid, 2-ethylhexanoic acid, nonanoic acid, 3, 5, 5 -Trimethylhexanoic acid, decanoic acid, neodecanoic acid, undecanoic acid, lauric acid, myristic acid, palmitic acid, margaric acid, stearic acid, arachidic acid, Linderic acid, tuzuic acid, petroceric acid, oleic acid, linoleic acid, linolenic acid And transition metal salts such as arachidonic acid, formic acid, oxalic acid, sulfamic acid, and naphthenic acid.

Examples of the transition metal complex include complexes with β-diketone or β-keto acid ester. The following can be illustrated as (beta) -diketone and (beta) -keto acid ester.
Acetylacetone,
Ethyl acetoacetate,
1,3-cyclohexadione,
Methylene bis-1,3-cyclohexadione,
2-benzyl-1,3-cyclohexadione,
Acetyltetralone,
Palmitoyltetralone,
Stearoyl tetralone,
Benzoyltetralone,
2-acetylcyclohexanone,
2-benzoylcyclohexanone,
2-acetyl-1,3-cyclohexadione,
Benzoyl-p-chlorobenzoylmethane,
Bis (4-methylbenzoyl) methane,
Bis (2-hydroxybenzoyl) methane,
Benzoylacetone,
Tribenzoylmethane,
Diacetylbenzoylmethane,
Stearoylbenzoylmethane,
Palmitoylbenzoylmethane,
Lauroylbenzoylmethane,
Dibenzoylmethane,
Bis (4-chlorobenzoyl) methane,
Benzoylacetylphenylmethane,
Stearoyl (4-methoxybenzoyl) methane,
Butanoylacetone,
Distearoylmethane,
Stearoyl acetone,
Bis (cyclohexanoyl) methane,
Dipivaloylmethane.

  Although any thermoplastic resin can be used as the base resin in which the above-mentioned oxidizing organic component and transition metal catalyst are dispersed, the above-described ethylene-vinyl alcohol copolymer is suitable. That is, by using an ethylene-vinyl alcohol copolymer as a base resin, the oxygen barrier property of this layer can be further enhanced, and at the same time, the adhesion property with the adhesive intermediate layer described above can be enhanced.

  In such an oxygen-absorbing resin layer, the oxidizing organic component may be used in an amount of 1 to 15% by weight, particularly 2 to 10% by weight, based on the ethylene-vinyl alcohol copolymer as the base resin. Preferably, the transition metal catalyst is blended in an amount of 10 to 1000 ppm, particularly 50 to 500 ppm in terms of metal.

  In the multilayer structure of the present invention having the layer structure described above, a layer structure in which an oxygen-absorbing resin layer is provided as a gas barrier layer is particularly suitable. That is, in the oxygen-absorbing resin layer, as the oxidation of the oxidizing organic component progresses, the oxygen-absorbing ability decreases, and thus the oxygen barrier property decreases. Since the adhesive intermediate layer is provided, the oxygen barrier property of the adhesive intermediate layer compensates for the decrease in the oxygen barrier property of the oxygen-absorbing resin layer, and can maintain an excellent oxygen barrier property over a long period of time. Because it can.

  In addition, in the oxygen-absorbing resin layer, low molecular weight components such as aldehyde are generated with the oxidation of the oxidizing organic component, and such low molecular weight components cause odor and coloration. Especially, this multilayer structure is used as a container. If used, the flavor of the container contents may be reduced. For this reason, in the aspect which provided the oxygen absorptive resin layer, it is suitable to mix | blend an odor trapping agent with the inner and outer layers, especially an inner layer.

  As such an odor scavenger, a porous inorganic material mainly composed of silicate, such as zeolite or activated clay powder obtained by acid treatment of smectite clay minerals such as montmorillonite, is particularly preferable. High silica zeolite (silica / alumina ratio of 100 or more), which is a ZSM5 type crystal, is excellent in so-called plastic-specific polyodor and oxidation by-product trapping performance. Such an odor scavenger is generally blended in the inner layer (or outer layer) in an amount of 0.5 to 10% by weight.

  In addition, the multilayer structure of the present invention can be provided with a regrind layer by utilizing the excellent adhesiveness of the adhesive intermediate layer, whereby resources can be reused. This regrind layer is a mixture of the same kind of scrap resin as the inner / outer layer resin generated during inner / outer layer molding or container molding in the virgin resin for inner / outer layer formation. It is provided between the layer and the adhesive intermediate layer, in particular between the inner layer and the adhesive intermediate layer.

  In the various layer structures described above, the thickness of each layer may be appropriately set according to the use of the multilayer structure so that the characteristics of each layer are sufficiently exhibited.

The multilayer structure of the present invention is suitable for use as a packaging material, and is provided for use as, for example, a packaging film or sheet, a cap, or a container (such as a bottle or a cup-shaped container).
This multi-layer structure has a known contrast condition except that a predetermined contrast distribution is formed in the adhesive intermediate layer and a molding condition is adopted so that a clear interface is formed between the two components. Molded. For example, using a number of extruders and injection machines according to the number of layers, the film or sheet, cap or container preform was formed by co-extrusion, co-injection, etc., and formed into a preform form. The product is formed into a bottle or cup-shaped container by subsequent secondary molding, for example, blow molding or plug assist molding.

The present invention is particularly effective for those in which the inner and outer layers are formed of a polyolefin resin and exhibits excellent oxygen barrier properties in addition to the excellent moisture resistance possessed by the polyolefin resin. Beverages such as beer, wine, fruit juice, carbonated soft drink, fruit, nuts, vegetables, meat products, infant food, coffee, jam, mayonnaise, ketchup, cooking oil, dressing, sauces, boiled dairy products It is also applied to packaging materials such as containers for filling various contents that deteriorate in the presence of oxygen, such as pharmaceuticals, cosmetics, and gasoline.
Moreover, since the multilayer structure of the present invention is excellent in transparency, it can be suitably used for packaging containers that require transparency.

  The invention is further illustrated by the following examples, but the invention is not limited to these examples.

1. Manufacturing method
[Preparation of oxygen-absorbing resin composition]
Ethylene vinyl alcohol copolymer (EVOH, Kuraray EP-F171B) as the base resin, cobalt neodecanoate (cobalt content 14 wt%, DICANATE 5000, Dainippon Ink & Chemicals, Inc.), and anhydrous maleic as the transition metal catalyst An acid-modified polybutadiene (acid value 29 gKOH / g, RICON 131MA5 manufactured by Sartomer) was prepared.
By mixing the base resin pellets and the transition metal catalyst with a tumbler, a 350 ppm transition metal catalyst in a cobalt amount was uniformly attached to the surface of the base resin pellets to obtain catalyst pellets.
Next, using a twin screw extruder (TEM-35B manufactured by Toshiba Machine Co., Ltd.) with a strand die attached to the outlet portion, the catalyst pellets were melt-kneaded at a screw rotation speed of 100 rpm and a molding temperature of 200 ° C. using a liquid feeder. The maleic anhydride-modified polybutadiene was dropped to 5 wt% with respect to the catalyst pellets and extruded from a strand die to prepare an oxygen-absorbing resin composition.

[Preparation of resin composition containing deodorant]
Using a twin-screw extruder (Toshiba Machine Co., Ltd. TEM-35B), polypropylene is melt-kneaded at a screw rotation speed of 100 rpm and a molding temperature of 200 ° C., and a synthetic feeder (Na-ZSM5 type manufactured by Mizusawa Chemical Co., Ltd.) is obtained using a powder feeder. Was added so as to be 5% by weight with respect to polypropylene and extruded to prepare a resin composition containing a deodorant.
In addition, B251VT made from prime polymer was used as polypropylene.

Measuring method
[Viscosity measurement]
For an ethylene vinyl alcohol copolymer (hereinafter abbreviated as EVOH) and a maleic anhydride-modified olefin resin (hereinafter abbreviated as AD) used for the adhesive intermediate layer, a capillograph (manufactured by Toyo Seiki Co., Ltd.) and capillary L / D = 10 / 1 (mm), and the melt viscosity was measured at a cylinder temperature of 200 ° C.

[Calculation of viscosity ratio]
A melt viscosity of 200 s ⁻¹ corresponding to the strain rate of direct blow molding was read from the melt viscosity curve obtained by the above viscosity measurement, and the viscosity ratio η _AB was calculated using the following formula.
η _AB = a / b
a: Melt viscosity of EVOH at 200 ° C. and shear rate of 200 s ⁻¹ b: Melt viscosity of AD at 200 ° C. and shear rate of 200 s ⁻¹

Evaluation methods
[Standard deviation of contrast distribution]
The body of the produced multilayer structure was cut with a cutter so as to be a 1 × 1 cm square, and a smooth cross section was obtained using an ultramicrotome (Leica 2050 SUPERCUTS) in the thickness direction under a −100 ° C. condition. . Next, deposition was performed with an ion sputtering apparatus (E-1045 manufactured by Hitachi High-Technologies Corporation) under conditions of a distance of 3 cm between the sample surface and the sputtering apparatus, an output of 15 mA, and a deposition time of 15 s. The deposited surface was observed with a scanning electron microscope (S-4800, manufactured by Hitachi High-Technologies Corporation), and the phase structure of the adhesive intermediate layer was photographed at an acceleration voltage of 5 kV and a magnification of 3000 times.
The resulting photos are from Adobe Photoshop Elements
Using version 2.0, normalization was performed by an “image → tone correction → equalization” command in the software screen. This is to darken the blackest pixel of the photograph as 0 and the whitest pixel as 255, and to darken the entire image within the range of 0 to 255, and to compare the contrast distribution in the vicinity of the interface under the same conditions It is.
Next, using the image analysis software WINROOF ver6 (manufactured by Mitani Corporation), the “distribution of the EVOH and AD interface in the adhesive intermediate layer is digitized by the“ measurement → manual measurement → concentration cross-section measurement ”command in the software screen, Standard deviation was determined.
Further, such image analysis was performed at 10 locations, the standard deviations were averaged, and those with a value of 65 or more were marked with ◯, and those with less than 65 were marked with ×.
When the interface is clear, the boundary between EVOH (white portion) and AD (black portion) is clear, and the width of the contrast distribution is wide. Conversely, when the interface is unclear, the boundary becomes unclear, and the width of the contrast distribution becomes narrow. In the present invention, the standard deviation value is used as an index indicating the width of the contrast distribution.

[Oxygen barrier evaluation]
The produced multilayer structure was put in a glove box and purged with nitrogen. Next, 1 cc of distilled water was placed in the multilayer structure, and heat sealed with a lid material using an aluminum foil as a barrier layer and sealed. This multilayer structure was sterilized by hot water shower type moist heat at 123 ° C. for 30 minutes, and stored at 30 ° C.-80% RH for 1 week. The oxygen concentration in the multilayer structure after storage was measured by gas chromatography (Shimadzu GC-8A) to evaluate oxygen barrier properties.
Oxygen-sensitive contents cause deterioration in quality The standard of oxygen concentration in the container is 1.5%, less than 1.0% is ◎, 1.0% to less than 1.5% is ○, 1.5% or more X.

[Delami evaluation]
The body part of the produced multilayer structure was cut into 3 × 3 cm pieces with a cutter, and it was evaluated whether or not the end part was delaminated. What did not delaminate was set as (circle), and what did delamination was set as x.

[sensory evaluation]
The produced multilayer structure was put in a glove box and purged with nitrogen. Next, 1 cc of distilled water was placed in the multilayer structure, and heat sealed with a lid material using an aluminum foil as a barrier layer and sealed. This multilayer structure was sterilized by hot water shower-type moist heat at 123 ° C. for 30 minutes, stored for 1 week at 30 ° C.-80% RH, the container mouth was opened, and sensory evaluation was performed by a panelist.
◎: Almost odorless ○: Slight odor (poly odor)
×: Strong odor is felt (unusual odor)

Example 1
Using a direct blow molding machine, a wide-bottle-shaped multilayer structure (bore diameter: 44 mm, internal volume: 125 cc) was produced under the conditions of a shell diameter of 15 mm, a core diameter of 13 mm, and a molding temperature of 200 ° C.
The layer structure is 4 types and 6 layers (container outside: polypropylene layer 50um / adhesive intermediate layer 25um / EVOH layer 35um / adhesive intermediate layer 25um / regrind layer 300um / polypropylene layer 250um: container inside).
The resin used is polypropylene (B251VT made by prime polymer), EVOH (Eval EP-F171B made by Kuraray), and the adhesive intermediate layer was dry blended by EVOH and AD (Admer QE840 made by Mitsui Chemicals) at a weight ratio of 7: 3. A blend resin was used.
Further, from the viscosity measurement described above, a = 1620 Pa · s, b = 450 Pa · s, and η _AB = 3.6.
When the acid modification rate of AD was measured by ¹ H-NMR, the peak intensity was small and clear quantification was difficult, but it was estimated to be 3.6 meq / 100 g or less from the peak area value.
The produced multilayer structure was subjected to an oxygen barrier property evaluation, a delamination evaluation, and a sensory evaluation by obtaining a standard deviation by the evaluation method described above.

(Example 2)
A multilayer structure was prepared in the same manner as in Example 1 except that the blending ratio of the blend resin used for the adhesive intermediate layer was changed to 5: 5, and standard deviation, oxygen barrier property evaluation, delamination evaluation, and sensory evaluation were performed. The results are shown in Table 1.

(Example 3)
The maleic anhydride-modified olefin resin (AD) was changed to Mitsui Chemicals Admer QE850, and an adhesive intermediate layer was formed using a blend resin (blend ratio 7: 3) of EVOH and AD in the same manner as in Example 1. Except for the above, a multilayer structure was prepared in the same manner as in Example 1, standard deviation, oxygen barrier property evaluation, delamination evaluation, and sensory evaluation were performed. The results are shown in Table 1.
The viscosity of AD was b = 320 Pa · s and η _AB = 5.1.
When the acid modification rate of AD was measured by ¹ H-NMR, the peak intensity was small and clear quantification was difficult, but it was estimated to be 3.6 meq / 100 g or less from the peak area value.

Example 4
A multilayer structure was produced in the same manner as in Example 1 except that a layer (oxygen absorbing layer) of an oxygen absorbing resin composition containing an oxygen absorbing agent was formed instead of the EVOH layer.
That is, the layer structure of this multilayer structure is 4 types and 6 layers (outside of container: polypropylene layer 50 um / adhesive intermediate layer 25 um / oxygen-absorbing resin layer 35 um / adhesive intermediate layer 25 um / regrind layer 300 um / polypropylene layer 250 um: Inside the container).
The produced multilayer structure was subjected to oxygen barrier property evaluation, delamination evaluation, and sensory evaluation. The results are shown in Table 1.

(Example 5)
Using a sheet molding machine, a multilayer sheet was produced under the condition of a molding temperature of 230 ° C. And the multilayer cup was produced using the plug assist vacuum pressure forming machine.
The layer structure of the used multilayer sheet is 5 types and 6 layers (outside: polypropylene layer 400 um / adhesive intermediate layer 70 um / oxygen-absorbing resin composition layer 60 um / adhesive intermediate layer 70 um / regrind layer 600 um / deodorant compounded resin) Layer 300 um: inside) and the total sheet thickness is 1500 um.
The adhesive intermediate layer was formed using a blend resin obtained by dry blending EVOH and AD (Admer QE840 manufactured by Mitsui Chemicals) at a weight ratio of 6: 4.
After cutting the multilayer sheet into 30 cm square, the inner and outer layers of the sheet are heated to 190 ° C. with a far-infrared heater, melt-formed using a plug-assist vacuum / pressure forming machine, and the drawing ratio H / D = 0.8, A cup-shaped multilayer structure having an internal volume of 180 ml during filling was prepared.
The produced multilayer cup was subjected to oxygen barrier property evaluation, delamination evaluation, and sensory evaluation. The results are shown in Table 1.

(Example 6)
Using a multilayer compression molding method in which various materials are extruded by an extruder and the cut molten resin lump (drop) is set in a compression mold and compression molded, the container weight is 6.0 g, and the internal volume at the time of full filling Produced a 66 ml multilayer cup.
The layer structure and thickness of each layer of the cup body are 3 types and 5 layers (outside: deodorant compounded resin layer 215um / adhesive intermediate layer 20um / oxygen-absorbing resin composition layer 30um / adhesive intermediate layer 20um / deodorant compounded resin layer) 215um: inside).
As the adhesive intermediate layer, a blend resin obtained by dry blending EVOH and AD (maleic anhydride olefin resin, Admer QF551 manufactured by Mitsui Chemicals) at a weight ratio of 5: 5 was used.
The produced multilayer cup was subjected to oxygen barrier property evaluation, delamination evaluation, and sensory evaluation. The results are shown in Table 1.

(Comparative Example 1)
A multilayer structure was prepared in the same manner as in Example 1 except that AD used for the adhesive intermediate layer was changed to Admer QB550, and standard deviation, oxygen barrier property evaluation, delamination evaluation, and sensory evaluation were performed. It was shown to.
Further, when the cross section of the multilayer structure was observed with a microscope, it was observed that EVOH and AD were compatible with each other in the adhesive intermediate layer to form a continuous phase.
Moreover, the viscosity of AD was b = 750 Pa · s and η _AB = 2.2.
When the acid modification rate of AD was measured by ¹ H-NMR, the peak intensity was small and clear quantification was difficult, but it was estimated to be 3.6 meq / 100 g or less from the peak area value.

(Comparative Example 2)
A multilayer structure was prepared in the same manner as in Example 1 except that AD was not used for the adhesive intermediate layer, and standard deviation, oxygen barrier property evaluation, delamination evaluation, and sensory evaluation were performed. The results are shown in Table 1. It was.

(Comparative Example 3)
A multilayer structure was prepared in the same manner as in Example 1 except that EVOH was not used for the adhesive intermediate layer, standard deviation, oxygen barrier property evaluation, delamination evaluation, and sensory evaluation were performed. The results are shown in Table 1. It was.

(Comparative Example 4)
A multilayer structure was prepared in the same manner as in Example 1 except that the blending ratio of the blend resin used for the adhesive intermediate layer was changed to 3: 7, and standard deviation, oxygen barrier property evaluation, delamination evaluation, and sensory evaluation were performed. The results are shown in Table 1.

(Comparative Example 5)
A multilayer structure is prepared in the same manner as in Example 1 except that the blending ratio of the blend resin used for the adhesive intermediate layer is changed to 9: 1, and standard deviation, oxygen barrier property evaluation, delamination evaluation, and sensory evaluation are performed. The results are shown in Table 1.

  As can be seen from Table 1, the viscosity and blending ratio of the blend resin used for the adhesive intermediate layer affect delamination evaluation and barrier properties. This is due to the phase structure of the adhesive intermediate layer. When the interface between EVOH and AD is clear, that is, when the standard deviation is 65 or more, good oxygen barrier properties are obtained without delamination. be able to. In addition, by having an oxygen-absorbing resin in the intermediate layer, it maintains a high oxygen barrier property even after retorting, and by providing a deodorizing layer in the innermost layer, it accompanies so-called plastic-specific polyodor and oxygen absorption It was confirmed from sensory evaluation that the odor derived from the oxidation by-product can be reduced.

Claims (11)

  A multilayer structure in which an adhesive intermediate layer made of a blend of an ethylene-vinyl alcohol copolymer (A) and a maleic anhydride-modified olefin resin (B) is provided between the inner and outer layers, The intermediate intermediate layer contains the ethylene-vinyl alcohol copolymer (A) and the maleic anhydride-modified olefin resin (B) in a weight ratio of 4: 6 to 8: 2, and the cross section in the thickness direction of the multilayer structure In the scanning electron microscope observation photograph of the above, using image analysis software, the contrast distribution in the vicinity of the interface between the ethylene-vinyl alcohol copolymer (A) and the maleic anhydride-modified olefin resin (B) in the adhesive intermediate layer A multilayer structure characterized by exhibiting a standard deviation of 65 or more when quantified.   The phase structure of the adhesive intermediate layer is a sea-island structure in which the maleic anhydride-modified olefin resin (B) is the sea, or any of the ethylene-vinyl alcohol copolymer (A) and the maleic anhydride-modified olefin resin (B). The multilayer structure according to claim 1, which is a bicontinuous phase existing as a continuous phase.   The multilayer structure according to claim 1, wherein at least one of the inner and outer layers is formed of a polyolefin resin.   A gas barrier intermediate layer comprising an oxygen-absorbing resin layer or an oxygen barrier resin layer is provided between the inner and outer layers, and the adhesive layer is adjacent to the inner layer side and the outer layer side of the gas barrier intermediate layer. The multilayer structure according to claim 1, further comprising a conductive intermediate layer.   The multilayer structure according to claim 4, wherein the gas barrier intermediate layer includes an ethylene-vinyl alcohol copolymer as a resin base material. In the adhesive intermediate layer, the ethylene-vinyl alcohol copolymer (A) and the maleic anhydride-modified olefin resin (B) have the following formula:
η _AB = a / b
Where a is ethylene at 200 ° C. and a shear rate of 200 s ⁻¹
The melt viscosity of the vinyl alcohol copolymer (A),
b is maleic anhydride at 200 ° C. and shear rate 200 s ⁻¹
The melt viscosity of the acid-modified olefin resin (B).
The multilayer structure according to claim 1, wherein the viscosity ratio η _AB defined by is in the range of 3-10.   The multilayer structure according to claim 1, which is a deodorant-containing resin layer in which an odor scavenger is added to the inner layer. From the outer layer to the inner layer, polyolefin layer / regrind layer / adhesive intermediate layer / oxygen-absorbing resin layer / adhesive intermediate layer / deodorant-containing resin layer,
Polyolefin layer / adhesive intermediate layer / oxygen-absorbing resin layer / adhesive intermediate layer / regrind layer / deodorant-containing resin layer,
2. The polyolefin layer / regrind layer / adhesive intermediate layer / oxygen-absorbing resin layer / adhesive intermediate layer / regrind layer / deodorant-containing resin layer. Multilayer structure. A multilayer structure in which an adhesive intermediate layer made of a blend of an ethylene-vinyl alcohol copolymer (A) and a maleic anhydride-modified olefin resin (B) is provided between the inner and outer layers,
The adhesive intermediate layer contains the ethylene-vinyl alcohol copolymer (A) and the maleic anhydride-modified olefin resin (B) in a weight ratio of 4: 6 to 8: 2.
The ethylene-vinyl alcohol copolymer (A) and the maleic anhydride-modified olefin resin (B) are represented by the following formula:
η _AB = a / b
Where a is ethylene at 200 ° C. and a shear rate of 200 s ⁻¹
The melt viscosity of the vinyl alcohol copolymer (A),
b is maleic anhydride at 200 ° C. and shear rate 200 s ⁻¹
The melt viscosity of the acid-modified olefin resin (B).
A multilayer structure having a viscosity ratio η _AB defined by   The phase structure of the adhesive intermediate layer is a sea-island structure in which the maleic anhydride-modified olefin resin (B) is the sea, or any of the ethylene-vinyl alcohol copolymer (A) and the maleic anhydride-modified olefin resin (B). The multilayer structure according to claim 9, which is a bicontinuous phase existing as a continuous phase.   The multilayer structure according to claim 9, wherein at least one of the inner and outer layers is formed of a polyolefin resin.